1. Field of the Invention
This invention in general relates to the field of data storage and retreival, including recording and micro-lithography, and in particular to data storage and retrieval systems incorporating flying diffractive near-field optical elements.
2. Description of the Prior Art
Guerra and Plummer in 1987 first described and broadly claimed the application of evanescent field, now sometimes known as near-field, optics to a flying head, with the head flying in proximity to a rotating data storage media. Total internal reflection (TIR) of light within a transparent body results in an evanescent field leaking beyond the body. The light and TIR are frustrated when another body is brought within the decaying evanescent field, as first demonstrated by Newton in the 1600""s and studied by hundreds of researchers over the years, up to this day. Images of the optical data in a compact disc obtained with the evanescent field from an Amici sphere are shown and described by Guerra in 1988. The effective numerical aperture NA can be greater than 1, and resolution increases accordingly as the wavelength xcex/2NA, the spot size of the writing laser decreases, and the storage density increases as the square of the ratio of the new NA as increased by the Amici sphere and the original NA of the existing objective lens.
Kino and Mansfield in 1991 dislcose a solid immersion optical microscope, and together with Corle a lithography system employing a solid immersion lens (SIL), and an optical recording system employing a solid immersion lens. Similarly, Mamin, Rugar, and Terris describe a SIL built into a slider for optical data storage (1996). The SIL is an aplanatic hemisphere or hyper-hemisphere illuminated such that some of the light is totally internally reflected, and an evanescent or near-field is created.
It will be recognized by those even casually skilled in the art that the use of such near-hemispheres, hemispheres, and hyper-hemispheres placed close to the object to increase the numerical aperture of an optical system, whether with near-field illumination or propagating illumination, is inherent to every microscope objective design since Abbe invented the homogenous immersion objective in 1878.
As disclosed in this specification, the advantages of diffractive optical elements (which includes by definition Fresnel optics) over their optical refractive counterpart are brought to bear on the construction and application of high numerical aperture and near-field optical microscope devices in the fields of micro-lithography, and in particular to optical data storage. (Optical here is meant to include the full electro-magnetic spectrum, such as microwaves or the far infra-red, for example.)
While the art describes a variety of recording media, there remains a need for improvements that offer advantages and capabilities not found in presently available instruments, and it is a primary object of this invention to provide such improvements.
It is another object of the invention to provide for a method of reading and writing utilizing evanescent field resolution.
Other objects of the invention will be obvious, in part, and, in part, will become apparent when reading the detailed description to follow.
The present invention discloses an optical assembly suitable for use with an optical medium for the storage and retrieval of data. The optical assembly comprises a source of illumination for providing a beam of optical radiation, an objective lens disposed in the optical path of the beam for redirecting the beam to the optical medium, and a diffractive optical element disposed between the redirected beam of radiation and the optical medium such that at least a portion of the redirected beam of radiation passes through a surface of the diffractive optical element and is reflected to the objective lens. Other features of the invention will be readily apparent when the following detailed description is read in connection with the drawings.